This invention relates to the field of converting methyl esters to corresponding acids. More particularly, it relates to an improved strong acid process for hydrolyzing methyl esters having carboxylic acid moieties containing 6 to 22 carbon atoms.
It is known that these methyl esters can be hydrolyzed by reacting with water under conditions of high pressure and temperature (e.g. 700 psi and 250.degree. C.). This requires very expensive equipment and presents a methanol flammability problem.
As a result, consideration has been given to converting such esters to acids by an acidolysis reaction wherein an ester of a first carboxylic acid is reacted with a second carboxylic acid in the presence of strong acid catalyst to produce the first carboxylic acid and the ester of the second carboxylic acid. This is a well known reaction and is described, for example, in Graves U.S. Pat. No. 1,882,808. Very often, the acidolysis is an acetolysis, that is, the replacing (displacing) acid is acetic acid. In the context of methyl esters of C.sub.6 -C.sub.22 carboxylic acids, this means reacting such ester with acetic acid to produce C.sub.6 -C.sub.22 carboxylic acids and methyl acetate. This reaction has the disadvantage in a commercial context of requiring disposal or separate hydrolysis of methyl acetate. Disposal is disadvantageous because consumed displacing acid is lost. Separate hydrolysis has the disadvantage of requiring a second process facility (a reactor and distillation units different from the reactor and distillation units used for the acetolysis) and also the drying of the resulting acetic acid before it can be reused.
It is an object of this invention to provide hydrolysis of the said methyl esters wherein relatively mild conditions of temperature and pressure can be used.
It is a further object of this invention to provide a process wherein displacing acid is not consumed, where no product ester need be disposed of, and where only a single reaction system (e.g. reaction vessel plus distillation means) is required.